1. Field of the Invention
This invention generally relates to an apparatus for recording both sides of a sheet of recording medium, and, in particular, to a high-speed both side recording apparatus capable of recording a first image on one side of a sheet of recording paper and then recording a second image on the opposite side.
2. Description of the Prior Art
A both side recording apparatus is well known in the art. In such a both side recording apparatus, there is defined a first transportation path which extends from a paper supplying station to a paper discharging station and also a second transportation path having both ends connected to the first transportation path to thereby form a feed-back loop. An image transfer station is disposed along the first transportation path so that a toner image is transferred from an image forming device to a sheet of recording paper which is being transported along the first transportation path, and an image fixing station is also disposed along the first transportation path downstream of the image transfer station with respect to the direction of advancement of a sheet of recording paper. Thus, the toner image transferred to a sheet of recording paper becomes permanently fixed to the sheet as the sheet travels through the image fixing station. Also provided along the first transportation path is a registration roller which is driven to rotate intermittently in association with the operation of the image forming device.
The first end of the second transportation path is connected to the first transportion path at a first location upstream of the location where the registration roller is disposed, and the second end of the second transportation path is connected to the first transportation path at a second location downstream of the location where the image transfer station is located. Thus, a sheet of paper being transported back through the second transportation path travels through the image forming and fixing stations for the second time so that image may be formed on both sides of the sheet. A paper inversion station is normally provided in the second transportation path so that the sheet is fed into the first transportation path as being turned upside down when supplied into the first transportation path from the second transportation path.
In such a double side recording apparatus, it is typically so structured that a sheet of paper is transported at the same speed both in the first and second transportation paths. However, since a sheet of paper undergoes an inversion process while being transported along the second transportation path so as to be fed back into the first transportation path for forming a second image on the opposite side, it takes some time for the sheet of paper to become ready for forming a second image, which is one of the main causes of a low copying speed of a both side recording apparatus.